Custom barrel for DT 300 Norma

[OfRoggeveen]

I'm new at this, so I'd like input on what the specifics need to be for a custom barrel. It'll be for a Desert Tech SRS rifle, primarily shooting 250 grain A-tips.

I read somewhere that a 1:7 twist is the fastest Hornady recommends for this bullet. But, when I plug that into a stability calculator, it tells me such a twist rate/load combination is only "marginally stable". So should I go with a 1:6, or 1:6.5? Or will the bullet come apart?

I'm planning on a 28"-30" barrel.

Thanks!

 

[cooper_257]

1:8 twist is plenty for the 250 A-tip 1:8.5 is good also.

 

[WeiserBucks]

1:8 twist is plenty for the 250 A-tip 1:8.5 is good also.

This, lots of this.

 

[Dogtown]

You may need to specify you want the throat cut to handle the 250s. They're pretty long bullets and I had trouble getting them to seat well in a standard throated barrel. So I had a new barrel made that was specifically throated for 250 A-Tips, and it's noticeably longer than the standard throat that I can't seat 220s without them jumping a significant amount.

And just to pile on, the 1:8 twist is good for the vast majority of bullets shot for this cartridge (200-250gr). The only reason I have a couple of 1:7 twist barrels is specifically to handle heavy solid bullets that are so long that they require a faster twist.

 

[OfRoggeveen]

1:8 twist is plenty for the 250 A-tip 1:8.5 is good also.

Can you explain to me why that is? Do the stability calculators need to be taken with a grain of salt?

 

[cooper_257]

Can you explain to me why that is? Do the stability calculators need to be taken with a grain of salt?

Hornady even states that 1:8.5 is enough. I would go with a 1:8 or if pushing them over 3000fps a 1:8.5. way over spinning jacketed bullets can cause issues.

 

[Dogtown]

You can’t really overspin solids, but jacketed bullets can disintegrate if spun too fast. How fast is too fast? Hard to say - it’s usually a combo of being a twist that is too fast and shot at significant velocity to really get the angular momentum high enough to exceed the bonds of the bullets

 

[secondofangle2]

I shoot 390 A-TIPS in a 1:12 375 barrel at 2900 fps. Granted, my DA is usually around 5000 ft, but they shoot lights out and they're "marginal" on the calculator and hornady recommends 1:11 (which Lilja doesn't do, so that was out).

And as noted above, while you can underspin a bullet (think subsonic 208 grain 308 cal in an 8" barrel with a can - oops!), you can also overspin it - not only can it disintegrate, but supersonic accuracy can suffer, according to Litz, because the angular momentum magnifies imperfections in the sectional density of the bullet

 

[Dogtown]

Yup, and there’s definitely a sweet spot for twist rate in a given load, but it’s not something most folks have the time/resources/sanity to trial and error to find it. “Good enough” is just that in most cases.

 

[waveslayer]

I'm running 1/8 just fine on my Norma, I've played with the 250's but stuck it out with the 230's... better velocity. Then my supply of 215's jumped up by 5K I may need to shoot those. But when I loaded with them, I had good results using n570 . Just couldn't justify the cost of them

 

[OfRoggeveen]

I'm running 1/8 just fine on my Norma, I've played with the 250's but stuck it out with the 230's... better velocity. Then my supply of 215's jumped up by 5K I may need to shoot those. But when I loaded with them, I had good results using n570 . Just couldn't justify the cost of them

What barrel length are you running? What velocities were you getting from the 250's?